An organic light emitting diode (OLED) display is a self-luminous display. Comparing with a liquid crystal display (LCD), since the OLED display does not require a backlight source, thus the OLED display is thinner. Further, the OLED display also has advantages such as high brightness, low power consumption, wide viewing angle, high response speed, wide operating temperature range, etc., and is increasingly applied in a variety of high-performance display field.
The luminescence mechanism of the OLED is that, under an external electric field, electrons and holes are injected into an organic light emitting material from positive and negative poles, they migrate in the organic light emitting material, recombine with each other and attenuate to emit light.
FIG. 1 shows a structure of an existing OLED device, which includes an anode layer 10, a cathode layer 20, and an organic functional layer 30 disposed between the two layers. The organic functional layer 30 may include a variety of functional layers including an electron transport layer 31, a hole transport layer 32 and an organic light emitting layer, etc. The organic light emitting layer usually includes organic light emitting materials of red, green and blue colors. As shown in FIG. 1, the organic light emitting layer may include a first light-emitting unit 331, a second light-emitting unit 332 and a third light-emitting unit 333 which can emit blue, red, green light, respectively.
The multi-layer structure of the OLED is to enable different functional layers to have different functions, so that various functions can be self-optimized. Interface properties between different functional layers are especially important. Since a heterojunction interface may include a plurality of complex physical mechanisms, such as energy conversion, carrier recombination, carrier separation, carrier injection, carrier accumulation, etc., thus queue time (Q-time) and process environment between different functional layers in a vacuum thermal evaporation process or surface treatment before the vacuum thermal evaporation process is especially important. The purpose is to generate a perfect interface between different materials which are used to form different functional layers.
Another existing hybrid OLED device is an OLED device, which is formed by two processes including a solution process and a vacuum thermal evaporation (VTE) process. Different materials are at two sides of an interface for different processes, respectively. During conversion of the two processes, heterojunction interface properties are necessarily affected, particularly the light emitting layers. For example, as shown in FIG. 2, in the OLED device, functional layers including the hole transport layer 32, the second light-emitting unit 332 and the third light-emitting unit 333 are formed through the solution process; thin film layers including the first light-emitting unit 331 and the electron transport layer 31 are formed through the vacuum thermal evaporation process. Since the first light-emitting unit and the second light-emitting unit as well as the third light-emitting unit are formed through different processes, thus functions of the first light-emitting unit and the second light-emitting unit as well as the third light-emitting unit will be affected.
Therefore, another OLED appears in the prior art. In the OLED, a hybrid connecting layer (HCL) formed through the vacuum thermal evaporation process is added in an interface where the solution process and the vacuum thermal evaporation process alternate. This can improve efficiency and lifetime of a first thin film layer formed through the vacuum thermal evaporation process. For example, as shown in FIG. 2, a hybrid connecting layer (HCL) 40 formed through the vacuum thermal evaporation process is disposed between the first light-emitting unit formed through the vacuum thermal evaporation process and the second light-emitting unit as well as the third light-emitting unit which are formed through the solution process. This can improve and enhance efficiency and lifetime of the first light-emitting unit.
However, the hybrid connecting layer (HCL) is required to not only play a role of transporting electrons in sub-pixels of the second light-emitting unit and the third light-emitting unit which are formed through the solution process, but also play a role of transporting holes in sub-pixels of the first light-emitting unit which is formed through the vacuum thermal evaporation process. Thus it is difficult to select materials for the hybrid connecting layer and it is also difficult to balance the carriers, thereby easily causing one of sub-pixels to emit a color of another sub-pixel.